Level 3
The average cost of some books is $75. When another 3 books are added, the total cost increases by $190. The average cost becomes $70. How many books are there in the end?
Level 2
There were 40 more dresses than blouses in a shop. After 70 dresses and 30% of the blouses were sold, there were an equal number of dresses and blouses left. How many blouses were there in the shop at first?